umm hmm 4-1 is illegal why. and 500 is a plenty for an exhaust or a part that will add a whole sum of 2 hp at the crank. but afterall it is your dads money. ok well i am liking the fireball by 5zigen. the world sport by dc is the quietest i think. and i heard a magnaflow on my friends maxima and it doesnt make any noise either. the choice is yours